A wave function describes the probability amplitude of a quantum system, allowing for the calculation of the probability of finding a system in a specific state at a given time. It is a mathematical construct that represents potential outcomes rather than a physical entity, and it does not propagate through space-time like classical waves. The Schrödinger equation, a partial differential equation, can be applied to quantum systems, including a simple pendulum, to determine energy levels through its time-independent form. The wave function's square gives the probability distribution for measurement results, emphasizing its role in quantum mechanics. Understanding these concepts is crucial for grasping the duality of light and the nature of quantum phenomena.